1. Field of the Invention
The present invention relates to a radio telecommunication apparatus such as a pager receiver, a mobile telephone, a cordless telephone, or the like, and more particularly to a radio telecommunication apparatus which can store messages it has received.
2. Description of the Related Art
In recent years a new type of a paging system has been developed, in which pager receivers display the messages transmitted from a base station. A paging signal used in this system is formed as follows. That is, one frame is time-divided into a plurality of groups each of which is time-divided into a synchronization word and a plurality of calling words. In each calling word are inserted an identification (ID) code and a message code.
In order to call one of the pager receivers which belongs to the paging system, a caller dials a telephone number assigned to the pager receiver, thereby calling the base station. Then, the caller transmits message data to the base station through the telephone line. Upon receipt of the telephone number and the message data, the base station generates an ID code from the telephone number and also a message code from the message data. The ID code is one assigned to the pager receiver which is being called. The ID code and the message code are inserted into a paging signal. More precisely, they are inserted into a vacant word of the group to which the pager receiver belongs. The paging signal containing the ID code and the message code is transmitted from the base station.
The pager receiver comprises an antenna, a radio circuit, a demodulation circuit, a control circuit, an ID code memory, a message memory, a drive circuit, a speaker, a liquid-crystal display (LCD), an LCD-driving circuit, a display switch, and a stop switch.
The antenna catches the paging signal transmitted from the base station. The paging signal is supplied via the radio circuit to the demodulation circuit, which demodulates the received paging signal. The demodulated signal is input to the control circuit. The control circuit compares the ID code contained in the paging signal, with the self-ID code stored in the memory. If the ID code is identical to the self-ID code, the control circuit outputs a ringing signal. The ringing signal is supplied via the drive circuit to the speaker. The speaker generates a ringing tone from the ringing signal. Hearing the ringing tone, the person having the pager receiver (hereinafter called "pager holder") knows that someone is calling him or her.
Upon the occurrence of a coincidence between the ID codes, the control circuit enters the message code received following the ID code. After being subjected to an error correcting process, the message code is decoded and the decoded message data is applied to a display driving circuit. Consequently the message is displayed on a liquid crystal display (LCD by the display driving circuit. Therefore, the pager holder can understand the message from the caller through the liquid crystal display at the time of generation of the call. The LCD stops displaying the message when the pager holder operates the stop switch or when a predetermined period of time elapses.
Meanwhile the message code is transferred from the control circuit to the message memory and is stored therein. The message code is read from the message memory and supplied to the control circuit, whenever the pager holder operates the display switch after the LCD has stopped displaying the message. Hence, the message can be displayed again.
Thus, every time the pager receiver receives a pager signal containing an ID code identical to the self-ID code, the LCD automatically displays the message represented by the message code inserted in the paging signal, and the message memory stores the message.
The message memory has a memory area large enough for storing six message codes at most. When the pager receiver receives a seventh message code, the first message code is erased from the message memory, whereby the seventh message code is stored into the message memory. Hence, as long as the pager receiver is used in ordinary conditions, the message memory always stores the latest six message codes the pager receiver has received.
The conventional pager receiver described above is disadvantageous in the following respect. At most six message codes are kept stored in the message memory up until the pager receiver receives a seventh message code. Therefore, if the pager receiver receives no message codes for several days or several weeks, the six message code stored in the message memory are several weeks or several days old. When the pager receiver receives a new message code very similar to, for example, the second oldest message code stored in the message memory, and the LCD displays the new message along with the old five messages, the pager holder may take the now oldest message for the new message.